Electrolytic method for the production of porous, catalytic metal



Nov. 9, 1948. M. M. MARlslc ETAL 2,453,668

ELECTROLYTIC METHOD FOR THE PRODUCTION OF POROUS, CATALYTIC METAL Filed June 2, 1944 PLAT/NG 54TH atentecl ov. 9, 1.948

` Aiipliatiim Jima 235;1944, seramos sagesse. @clamer (cisti-149i found that porous metal bodies.foilihiglmstructuralt:r

strength and great catalytic activity may'b.:pro"`" duced by a process of electrolytic'depositiofsdeV scribed hereinafter. w

The electrolytic deposition :.off metalsitosform: smooth, adherent coatings" requirsthefcntrorotf a number of variables which are as follow'sf-*S l. Current density. 2. Agitation of plating solutionj 3. Concentration of plating solutio i. 4. Temperature of plating solutiiif" Excessive "1i current; densitie"5M teniu "iatures ariel/or` concentrated fsrolut'i 4stresl i sL i1 porous' platings'-jwlii'cli""peel readily? ay b rubbed"A olf" very' f easily? Failures tot agitat* electrolyti'c solution-i or a toflovVrte olla""glta'tloii:` permitsthe accumulation of ibiibbl'siofhyd'r gason' theCathode'2:1,i1dtlls,L thier'eiius flll pitted l'and' :non-adherent* plating: u Low' current densities' with`iver'y"dilutelsoliit ns resultin: pf"zr rous platings. Such`plating"s"aeknown the" art, chiey because theyfareftofbe avoided. Obviously, they have not attained commercial use.

Electrolytic platings of-4 a*v porousfrrture pre duced` under; th'eea'bovefconditions y1eltl"fellilcient;Y metallic-'catalysts Platinum blackfis-suchfafcati" @institut-neuss as-a=fcata1yst has lbeerrl @dito-i academic interests becauset'of i" its"noneadh-er`-elif" quality. This disadvantage explains Whyporous". metallic platings have not found-practical: use as Y catalysts. t ,y

'I'his invention has for itsfpurpse.-aimethodu of preparing metallic catalysts which .involfvesfv alternatively plating metals byelect'rolytic means at conditions which produce `aS-porous-fplatingollowed by a smoothV adherent platingziand ssoffon, to build up a multiplicity of porousandfesmooth layers. The thickness of eachjslaylerz` may? be varied throughout wide ,limitss howeverf-iafrthickb ness of "a 100'. to :1000 metallic i atoms forV each-ff. layerlappears to be satisfactoryfromfthe'fpracticalfl* standpoint.

In :this process,` Econtrol of -pH is" much lessjirnf portantgthan is; thecaseiwhenshiny deposits "are desired." Inallneases, ittwasqfound tha1jpI-I.may` varyfwidelyfwithout material Veff ect onfthe. nature l of deposit according-.to lthe presentinvention.

coating-f;-A follovvech1 by.Y plating g' at a vhigh currentff density, for a-notltier:` short finterval of time, :and F ggf ,fone Thezfintervals "of: time? at Iwhich the---two`4 y typjes-iofrplatingfareconducted-maybe equalorl they? m'ayir beif 'variedf considerably: t

i-mother'lmethod,` involvesr plerio dical'lyfagita'ting or-circulatingliithe ielectrolyticisolution:to lbuild #upv successive porous and non-porous layers; Still another? procedure `:consists: :of moving ,fthe ^catlr odefperiodicailyi from? tlre relectrolytic bath maine tain'edratrodnoiternperaturefftofanother :bath'fxh'eld f at-'an elevtedetemperature: Or; thefftwo elece trolfyto'/bathsV may" be* composed: of.: solutions 1 of i di-errentconcentrations 4thefoneoathzcontaining a ysolutioniwhich giveszithef; sin'ootlliiplati'r'ig:` while. the: thericontainsi-a coneentratedafsolutiorrwhich. will? reswlftiinf-a orousfplatin'gtf Y Otherfm thirds:` ofi` producing `the Loatalysts -of this-.fin/vention* are illustrated-in thef sp'ecic' eX-I arliples.i They-'involveplatingfrornan"electrolytc bathl at current-.densitywhichproduces `afsrno'otrry coating and* simultaneously? iinpressing'fY suddeni surgesfof l exceedingly"v high =`Voltages -Ia't iish'ort {infJ tervals off'ftime- Thusgwlowe'r current* densities" are required to produce porous; adherentplatings tlrafiw'aenecessaryIwhen* low-i 'voltages 'i are emi plotted? The* presence "of suspensions the` elec#- precipitateattlotvficurrent d'rr'sitiesresults n` i spongy, adherent platings. Metals which arenonr-'f porous and not-catalyticmayfbe converted into porous catalysts by deplating and replating in a suitable electroiytic that-hr1' This flatter method offers ai meanszo regen-eratingfgthe spenticataliystsv oLthfisf-inventionr Apparatus fior preparingf the` catalytic 'f piorousf'- metals"folA thislfiivention-i-is `sl'iownint the 4tirati/ringer:

annexed: hereto, Whereinca Figures-1 is a* diagrammatic. illustrati'c'm` .ofnfapef` paratus for plating at regularly variedcurrezrtl Figure 2 is a diagram of'apnaratus"functioingu 3 in similar manner but having a different type of control.

Referring particularly to Figure 1, an anode I'EI and a cathode I I are immersed in an electrolytic plating cell I2. A primary battery I3, Or other source of D. C. potential, is connected to the anode and cathode through an ammeter HI and a variable resistance I5. The potential applied across the cell l2 between anode I0 and cathode Il is adjusted and correlated to composition of the bath, temperature, etc., to plate the desired metal from the bath on the cathode as a smooth adherent layer. A secondary battery IE is also connected across the plating bath in a circuit which includes resistance I1 and discharge tube I8. A condenser I9 is connected in parallel with the battery I6 and resistance I'I. The condenser is charged at rate depending on the electromotive force applied by the battery I6 or its equivalent, the resistance of element I'I and the capacity of the condenser until the potential across the condenser reaches the breakdown'potential of tube I8. A surge of current will then flow, discharging the condenser until the potential across the latter drops to the cutoiT potential of the tube, whereupon flow in the secondary circuit will cease and the cycle begun again.

Flow of current from the secondary battery will result in excessive evolution of hydrogen at the cathode, causing the metal plated to be highly porous. Since periods of deposition of soft porous metal alternate with periods of deposition of hard smooth metal, the resultant is a coating that is hard and adherent but highly porous, consisting of alternate layers of spongy and smooth metal. In this manner, the invention provides the high catalytic activity of porous plated metal with the tenacity and strength of smooth plated metal and the composition is suitable for commercial use.

According to the embodiment of Figure 2, currents of different potential are alternately applied between anode and cathode 2l across a plating bath 22 from different sources by a mechanical timing device. The primary, low potential circuit includes battery 23 and variable resistancel 25; While the secondary high potential circuit comprises battery 26 and variable resistance 21. The tWo circuits are connected in parallel across the plating bath through an ammeter 24 and a driven commutator 28. The commutator is adapted to alternately apply high and low potentials across the bath either by alternately closing the primary circuit and the secondary circuit or by maintaining the primary circuit closed while alternately opening and closing the secondary circuit.

The invention will be further understood from specific examples given below comparing catalysts prepared according to the invention with catalysts prepared by other methods of electroplating.

EXAMPLE I A hard, shiny, non-porous nickel plate was produced on a steel screen by connecting the screen as cathode in a conventional plating setup, using an aqueous bath of pH 4 to 5 containing 0.30 N. NiSOi, 0.08 N. NH4Cl and 0.08 M. I-IsBOs. A current density of 1 ampere per square decimeter was applied and the bath vigorously agitated.

This plating was tested as a catalyst and was found to possess very little activity.

EXAMPLE II A hard, shiny, somewhat porous nickel plate containing a very large number of tiny pinholes in its surface was obtained by using the following conditions;Vv pH=2.0-2.5 c. d.=1.0 amp/dm.2

`Wt. deposit: 0.8 gram Time of plating: 31/2 hours Solution concentrations:

0.15 N. NiSO4 v0.04 N. NH4C1 0.04 M. HsBOs The eiiect of this very acid solution was to produce a large number of very small hydrogen bubbles, which resulted in the pinholed type of p lating. This plate was tested as a catalyst for the hydrogenation of C2H4, and Was found to bel a better catalyst than a shiny, smooth plate, but not as good as the porous plating of the preferred portion of this invention.

EXAMPLE III c. d.=1.5 amp/dm.2 @Hlt-5.5

`Agitation--slight The overvoltage surges are obtained by a suitable timing arrangement. The positive pole of thehighvoltage source is connected to the positive pole of the plating cell. A diagram of the cell is shown in Figure 1. The effect of the surges of high voltage is to produce a Very large number `of tiny hydrogen bubbles which cause the plate deposited bythe steady lower current to be porous. This plate was a very active catalystl for the reduction of C2H4.

EXAMPLE IV Tough, porous, catalytically active plates may be obtained by plating from a solution containing a suspension of a precipitate, as for example, silica precipitate. Such a plate was obtained by using the following conditions:

pH=5.6-6.0 c.'d.=1.5 amp/dln.2 f Time of plating: 21A; hours Wt. of plate: 0.68 gram Agitation: Very vigorous Concentration of suspended `SiOz ppt. 1% Concentration of plating solution:

0.30 N NiSO4 -The silica gel was maintained in uniform suspension by vigorous stirring. It caused the hydrogen evolved on the cathode to be trapped on the surface and thus resulted in a porous plate.

genationcf C2H4.

EXAMPLE V A porous, tough, catalytically active nickel plated surface may be obtained by electrodepositing a heavy, smooth, uniform plate on an object, and then reversing the poles of the cell and plating part of this deposit off the object. This is accomplished by plating a smooth surface on the cathode by a known method. Then the plated cathode is placed in a bath at pH='1.0-2.0, and it is made the anode. Metal is removed partially at a current density of 0.5-5.0 amps. per dm?. It was found that almost any pH could be used with any current density, however, in practice, values are chosen which are most economical. The surface resulting from this treatment is very hard, porous, and adherent to the object on which plated. This plate was a very active catalyst for the reduction of CzHi.

EXAMPLE VI This example illustrates a method of regenerating the metallic catalysts of this invention when they have aged as a result of normal use in a catalytic process. The method of this example is applicable to the manufacture of new catalysts asit is obvious from the description below.

A porous nickel plated steel gauze which has been used as a hydrogenation catalyst and whose surface was partially sintered and catalytically inactive, was washed thoroughly with organic solvent to remove accumulated hydrocarbons, and ignited in air to remove carbon, and then reduced in H2 at 500 C. The catalyst is then placed in an electroplating cell, and made the anode.

c. d.=3.0 amps/dm.Z Concentration of solution:

0.15 N. NiSO4 0.04 N. NH4C1 0.04 M. H3BO3 As the current ows through cell, part of the spent plate is removed from the steel gauze, exposing fresh nickel surfaces. The catalyst is then made the cathode, the pH of the bath adjusted with aqueous ammonia, and a porous, adherent, catalytically active surface plated on at pI-I 5.0, and a current density of 1.0-1.5 amps/ dm?. It is noted that catalyst regeneration by this method results in 100% recovery of the catalyst metal.

EXAMPLE VII A porous, adherent, catalytically active nickel plate may be produced by plating alternately at current densities which produce smooth and porous plates for short intervals of time, as 5-20 seconds. In this example the following conditions were used:

pH=4.5-5.5 c. d. alternately for 5 seconds:

1.0 amp/dm.2 2.0 amp/dm.2 Agitation: very slight Concentration of solution:

0.15 N. NiSOl 0.04 N. NH4C1 0.04 M. HsBOa A timing device was used to control the current density. Figure 2 is a diagram of this type of plating dell.' h'alternatsmoth plating onto the porous layers leads to a very adherent but porous surface. This plate was found to be an excellent catalyst for the hydrogenation of 02H4.

The periods of plating under the different current densities need not'be equal. Very good results were obtained when the ratio of smooth to porous plating times varied between 1 to 1 and 1 to 4. For example, good, adherent catalytic plates were formed by plating at lamp/dm.2 for 5 seconds and4 at 2 amp/dm.2 for 5, 10, 15 or zoseconds.

The catalytic properties of the catalysts prepared in the above examples were evaluated by testing their efciency in `hydrogenating ethylene. Equal volumes of hydrogenl and C21-I4 were rea cycled overthe catalysts at to 155i* C. and atmospheric pressure for 5 minutes, and then arlaiyzfed.l Approximately the same weight of catalyst wasused in each experiment. The relative emergencies ef the catalysts are shown in Tablel: Y

i Table 1 Catalyst Unplated Steel xample I. Example II Example III. Example IV- Example V- Example VI Example VII EXAMPLE VIII Catalytically active cobalt surfaces are useful in treactions such as the hydrogenation of carbon monoxide by the Fischer-Tropsch process. In such an exoth'ermic process, they afford an excellent means of heat transfer and hence heat control.

In general, hydrogenation of carbonaceous substances may be conducted in the presence of nickel, cobalt and iron catalyst prepared according to the present invention,

We claim:

1. The process for producing a porous catalytic metallic body consisting of a plurality of alternate layers of dense and porous nickel, which consists in the electrodeposition of nickel by imposing a current having a density of approximately 1.5 amperes per square decimeter across the .electrodes of an electrolytic cell containing an aqueous electrolytic bath of 0.30 N. nickel sulfate having a pH between about 4.6 and about 5.5, maintained at substantially room temperature, to effect the deposition of a smooth, dense layer of nickel, simultaneously imposing from a high voltage source, the poles of which are connected to poles of like charge of said electrolytic cell, sudattacco den surges of overvoltage of between about '75 and about 80 volts at intervals of between about 0.5 and about l second to produce during the imposition of said overvoltage the deposition of a porous nickel layer, thereby effecting, as a re sult of said surges of overvoltage upon the steady lower current, an alternate deposition of smooth and porous layers of metallic nickel to yield a resulting composition characterized by high structural strength.

2. The process for producing a porous catalytic metallic body consisting of a plurality of alternate layers of dense and porous nickel, which consists in the electrodeposition of nickel by irnposing a current having a density of approximately 1.5 amperes per square -deciineter across the electrodes of an electrolytic cell containing an aqueous electrolytic bath of vnickel sulfate, boric acid, and ammonium chloride having a pH between about 4.6 and about 5.5 to eiect deposition of a smooth, dense layer of nickel, simultaneously imposing from a high Voltagesource, the poles of which are connected to poles of like charge of said electrolytic cell, sudden surges of overvoltage of between about 75 and about 80 Volts at intervals of between about 0.5 and about 1 second to produce during the imposition of said overvoltage the deposition of a porous nickel layer, thereby effecting, as a result of said surges 82, of overvoltage upon the steady lower current, an alternate deposition of smooth and porous layers of metallic nickel to yield a resulting composition characterized by high structural strength.

MILTON M. MARISIC. THOMAS F. RUTLEDGE.

REFERENCES CITEDl The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 485,343 Fletcher NOV. 1, 1892 585,359 Hopfner June 29, 1897 1,151,003 Ellis Aug. 24, 1915 1,527,734 Huggins Feb. 24, 1925 2,026,466 Grolee Dec. 31, 1935 2,046,440 Adey July 7, 1936 2,098,960 Frey Nov. 16, 1937 2,116,927 Germer May 10, 1938 2,138,881 Pyzel Dec. 6, 1938 2,206,908 Lunt July 9, 1940 2,297,817 Truxell etal Oct. 6, 1942 2,387,772 Ruben Oct 30, 1945r FOREIGN PATENTS Number Country Date 23,347 Great Britain Oct. 15, 1913 

